1. Field of the Invention
The present invention relates to novel compounds useful as agricultural or horticultural fungicides, a process for their preparation and fungicides containing the same.
2. Description of the Background
Modern agriculture enjoys high productivity depending upon fertilizers, agricultural chemicals and various agricultural tools and materials. On the other hand, there have been serious problems such that resistant microorganisms have been created by continuous use of agricultural chemicals, and plant diseases have been created by continual cultivation of the same crop plants. Under these circumstances, it is strongly desired to develop new and highly safe agricultural chemicals. The present invention provides a means for solving such problems. The present invention provides a dicyanopyrazine compound of the formula: ##STR2## wherein each of R.sub.1, R.sub.2 and R.sub.3 is hydrogen, lower alkyl, lower alkenyl, lower alkynyl, cycloalkyl, aralkyl, substituted aralkyl or thienylmethyl, provided that R.sub.1, R.sub.2 and R.sub.3 are not simultaneously hydrogen and that at one of R.sub.1, R.sub.2 and R.sub.3 is an alkyl group having four or more carbon atoms. The present invention also provides a process for preparing a compound of the formula I which comprises reacting a compound of the formula: ##STR3## wherein R.sub.1 is as defined above, with a compound of the formula: EQU R.sub.2 NR.sub.3 H (III)
wherein R.sub.2 and R.sub.3 are as defined above.
Further, the present invention provides an agricultural or horticultural fungicide which comprises an effective amount of the compound of the formula I as defined above and a carrier or diluent.
Now, the present invention will be described in detail with reference to the preferred embodiments.
Among the compounds of the formula I, particularly preferred are those wherein R.sub.1 is hydrogen, C.sub.1 -C.sub.5 alkyl, propenyl or propynyl; R.sub.2 is C.sub.4 -C.sub.5 alkyl, C.sub.3 -C.sub.5 alkynyl, C.sub.5 -C.sub.7 cycloalkyl, benzyl, chlorobenzyl, methylbenzyl, ##STR4## or thienylmethyl; and R.sub.3 is hydrogen or C.sub.1 -C.sub.4 alkyl.
The diamino dicyanopyrazine compounds of the present invention can readily be prepared as shown by the following reaction scheme: ##STR5##
In the above formulas, each of R.sub.1, R.sub.2 and R.sub.3 is hydrogen, lower alkyl, lower alkenyl, lower alkynyl, cycloalkyl, aralkyl, substituted aralkyl or thienylmethyl.
The 2-chloro-3-substituted amino-5,6-dicyanopyrazine obtained by the process of the formula (1) includes known compounds (vide U.S. Pat. Nos. 3,879,394 and 4,054,655). From such dicyanopyrazine, the compound of the formula I of the present invention can be obtained by the process of the formula (2).
This reaction is preferably conducted in an ether solvent such as tetrahydrofuran, dioxane or diethyl ether or in a polar solvent such as N,N-dimethylformamide or dimethylsulfoxide. Such solvents may be used alone or in combination as a mixture.
The reaction temperature is usually within a range of from 0.degree.to 150.degree. C., preferably from room temperature to 60.degree. C. Suitable reaction conditions may easily be selected by those skilled in the art.
When the compounds of the present invention are to be used as fungicides, they may be combined with various carriers in accordance with common techniques for the preparation of agricultural drug formulations and may be used in the form of various formulations such as a wettable powder, an emulsifiable concentrate, a dust, a granule or a dispersion.
Among carriers, liquid carriers may be the usual organic solvents, and solid carriers may be the usual clay minerals, pumice, etc. Further, a surfactant may be added to impart emulsifability, dispersibility or spreadability to the formulation. Further, it may be used in combination with a fertilizer or other agricultural chemicals such as insecticides or other fungicides.
When used as a fungicide, the active compound must be applied in a sufficient amount so that the desired effects can be obtained. The dose is usually within a range of from 50 to 2,000 g/ha, preferably from 200 to 1,000 g/ha. The compound of the present invention is used usually in the form of a formulation such as a wettable powder, an emulsifiable concentrate, a dust, a granule or a dispersion, containing from 0.1 to 50% of the active ingredient.
To prepare an emulsifiable concentrate, the active ingredient is dissolved in an agriculturally acceptable organic solvent, and a solvent-soluble emulsifier is added thereto. As a suitable solvent, xylene, o-chlorotoluene, cyclohexanone, isophorone, dimethylformamide, dimethylsulfoxide or a mixture thereof may be mentioned. Particularly preferred is a solvent mixture comprising an aromatic hydrocarbon or an aromatic hydrocarbon and a ketone and a polar solvent.
The surfactant used as an emulsifier usually constitutes from 1 to 20% by weight of the emulsifiable concentrate and may be cationic, anionic or non-ionic.
Anionic surfactants include alkyl sulfates, alkyl diphenylether disulfonates, naphthylmethane sulfonates, lignin sulfonates, alkylsulfo succinates, alkyl benzene sulfonates and alkyl phosphates. Cationic surfactants include alkylamines and quaternary ammonium salts. Non-ionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkyl aryl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerol fatty acid esters and polyoxyethylene fatty acid esters.
The concentration of the active ingredient is usually within a range of from 0.5 to 20% by weight, preferably form 1 to 10% by weight.
The wettable powder is formulated by adding an active ingredient to a finely pulverized inert solid carrier and a surfactant. The active ingredient is incorporated usually within a range of from 2 to 50% by weight and the surfactant is incorporated usually within a range of from 1 to 20% by weight.
The solid carrier commonly used for the combination with the active ingredient includes a naturally produced clay, a silicate, silica and an alkaline earth metal carbonate. Typical examples include kaolin, zeaklite, talc, diatomaceous earth, magnesium carbonate, calcium carbonate and dolomite.
As commonly employed emulsifiers, extenders, or dispersants, anionic surfactants, non-ionic surfactants or mixtures thereof may be employed. Those similar to the surfactants mentioned above for use for an emulsifiable concentrate may be employed.
The dust formulation is prepared by mixing the active ingredient with an inert carrier commonly employed for the preparation of dust formulations, such as talc, finely pulverized clay, pyrophyllite, diatomaceous earth or magnesium carbonate.
The concentration of the active ingredient is usually within a range of from 0.1 to 20% by weight, preferably from 0.5 to 5% by weight.
The granule formulation is prepared by mixing the active ingredient with a finely pulverized inert carrier such as bentonite, kaoline clay, diatomaceous earth or talc, kneading the mixture with water and then granulating it by a granulating machine. Otherwise, the granule formulation may be prepared by impregnating the active ingredient dissolved together with an extender to a granular carrier preliminarily granulated to have a particle size within a range of from 15 to 30 mesh or to a granular mineral prepared by pulverizing natural pumice, acid clay or zeolite and adjusting the particle size range. The active ingredient in such a granule formulation is usually within a range of from 0.2 to 20% by weight, preferably from 1 to 10% by weight.
The dispersion is prepared by finely pulverizing the active ingredient and mixing it with a surfactant and water. As the surfactant to be used, the anionic surfactants, cationic surfactants and non-ionic surfactants mentioned above for use in an emulsifiable concentrate may by used alone or in combination. The amount of use is usually within a range of from 1 to 20% by weight.
The active ingredient is usually within a range of from 1 to 50% by weight, preferably from 2 to 20% by weight.
Now, the present invention will be described in further detail with reference to examples. However, it should be understood these examples are provided for purposes of illustration and the present invention is by no means restricted by such specific examples.